Federal health officials are under fire for their unclear public warnings after one death and nearly 200 cases of vaping-related lung illnesses, which some say are related to the far riskier practice of vaping marijuana oil rather than nicotine.

Some state health department and news reports suggest many of the cases of lung problems involve tetrahydrocannabinol, known as THC, the chemical in marijuana that causes psychological effects.

Boston University public health professor Michael Siegel said the Centers for Disease Control and Prevention is being “unnecessarily vague” about describing the injuries as simply vaping-related when many people might have been injured by vaping THC oil.

“Based on what we know now, I think there’s enough to tell people: Don’t vape THC oils – especially products that are bought off the street,” Siegel said. "There are certain things the agency could be recommending right now that could potentially save lives and prevent this from happening by being much more specific.”

Dylan Nelson of Burlington, Wis., with his sister, Andrea, was rushed to the hospital with severe breathing problems after he vaped nicotine and THC oil. Doctors put him into a medically induced coma and hooked him up to a ventilator.(Photo: Rick Wood / Milwaukee Journal Sentinel)

The CDC, the Food and Drug Administration and state health agencies say they are completing the painstaking work of tracing common factors that may have triggered the spate of vaping-related lung illnesses mainly harming young adults.

Siegel acknowledged he is not privy to all the information the CDC has gathered. The agency probably does not know whether THC is the only culprit, he said, but the public would likely benefit if the agency warned vapers to avoid THC oil.

Michael Siegel is a professor in the Department of Community Health Sciences at the Boston University School of Public Health.(Photo: Boston University)

“There are millions of people vaping out there,” said Siegel, who supports vaping as a way for adults to quit smoking. “When they get this advice ‘Well, we don’t know what it is; it’s vaping,’ that doesn’t help anyone. So I think they need to try to be specific."

Most nicotine-laced liquids in e-cigarettes are alcohol-based and can't cause "lipoid pneumonia," the type cited in many of the lung cases, according to Siegel. The oil used when marijuana is vaped can, he said.

New York University public health professor Ray Niaura said the spate of lung illnesses means "it is unlikely it is e-cigarettes that have been on the market for a long time" unless "something was either changed or a new product was introduced into marketplaces." Niaura also supports vaping for smoking cessation by adults if the proper safeguards are in place for the products.

Ray Niaura is a professor in the College of Global Public Health at New York University and interim chair of its Department of Epidemiology.(Photo: New York University.)

"If it’s nicotine, it’s like a bad batch or a new player that is unknown," says Niaura, a former science director at the anti-tobacco Truth Initiative. "More likely, it’s what others are saying and people are vaping a lot of other things besides nicotine, such as synthetic cannabis or contaminated THC that is making an appearance and leading to these bad consequences."

Harris said she advises people to avoid vaping THC products – or any vaping product that contains oil – because research suggests that can be a risk factor for lipoid pneumonia.

"If somebody is going to insist on vaping, use the products that are from a reputable place and don’t add extra material to your vaping," Harris said.

The vaping industry blamed tainted THC sold by unlicensed retailers. The American Vaping Association wants federal officials to clarify where the problems lie.

One of the challenges for investigators is that teens and even some adults "are going to be reluctant to disclose the use of THC to their parents or doctors," said Gregory Conley, president of the vaping association. He said his group was contacted by a patient with one of the less serious respiratory illnesses who said he was only vaping THC, but he worried going public would jeopardize his college scholarship.

"The truth is that in every case so far in which a specific e-liquid has been identified, that product has been a THC-containing e-liquid, typically purchased off the street and often in open cartridges such that they could contain a contaminant or other drug," Siegel said.

Siegel noted that in at least some of the cases, the use of a THC oil, such as butane hash oil, was blamed. In January, someone vaping butane hash oil developed severe acute respiratory illness that was attributed to the hash oil.

The CDC and Food and Drug Administration officials defended themselves Friday, telling reporters the investigations are time-intensive and are being conducted in cooperation with states.

Dr. Brian King of the CDC's Office on Smoking and Health told reporters that harmful ingredients in traditional nicotine vape liquid had been identified that included ultrafine particulates, heavy metals such as lead, cancer-causing chemicals and flavoring used in e-cigarettes to give it a buttery flavor.

Those ingredients had been related to severe respiratory illness, he said. While they haven't been linked to the current cases, "we know that e-cigarette aerosol is not harmless," King said.

Though the government knows people use substances including THC in vape pens, King said, "the bottom line is there’s a variety of things in e-cigarette aerosol that could have implications for lung health."

Public health investigators need to gather more information about each case, including details such as what substances and products triggered the lung illnesses, said Mitch Zeller, director of the Food and Drug Administration's Center for Tobacco Products.

He noted that "many of these cases have involved the presence of compounds like THC, and we need to get to the bottom of every single case."

In a statement, Juul said it was monitoring the reports. The e-cigarette maker added that "reporting also suggests many patients were vaping both nicotine and THC" and underscores the importance of keeping tobacco and nicotine products away from young people.

"We also must ensure illegal products, such as counterfeit, copycat, and those that deliver controlled substances, stay out of the market," the statement said.

Monday, the California branch of the National Organization to Reform Marijuana Laws warned consumers not to buy THC vape products from unlicensed retailers.

Kim Barnes, Dylan Nelson's mother, urged other families to come forward if their loved ones have suffered similar injuries to prevent more people from getting sick.

"I don't want somebody else's son to end up like this," Nelson's mother, Kim Barnes, told the Milwaukee Journal-Sentinel. “That's why when they told me I just thought, ‘Well, why isn't anybody saying anything about this?’"